The subject matter of the present invention is a method for the production of anhydrous potassium tert.butoxide by the reaction of aqueous potash lye with tert.butyl alcohol in a packed distillation column, in which the water is distilled out at the top using a withdrawing agent, and in the sump of the column, which is kept at the boiling temperature, an alcoholic solution of the potassium tert.butoxide is produced, which is continuously withdrawn and is then processed for the recovery of the potassium salt.
The preparation of potassium tert.butoxide, which is generally called potassium tert.butylate, from metallic potassium with anhydrous tert.butyl alcohol, is described in Houben-Weyl, Vol. IV/2 (1963), pp. 7-8, where mention is also made of the possibility of operating in an inert solvent. This procedure, however, has the disadvantage that the metallic potassium used is difficult to handle, and that the absolutely water-free tertiary butyl alcohol that is needed to achieve an end product of perfect quality is difficult to produce.
Even in the case of the known transalcoholization of a lower alcoholate with the desired higher alcohol, it is necessary, in order to produce anhydrous potassium tert.butoxide, to have an absolutely water-free tert.butyl alcohol, which is very difficult to produce in pure form. Also, in the case of the transalcoholization of lower potassium alcoholates with tert.butyl alcohol, the equilibrium is very strongly on the side of the starting substances, so that only a great excess of tert.butyl alcohol will lead to reasonable yields. This excess necessitates the boiling up of large amounts of butanol, which considerably increases the expenditure of energy required by this process.
The above disadvantages are largely removed by the process described in German Federal Pat. No. 968,903: the reaction water is distilled azeotropically and thus removed from the system. This process, however, has the disadvantage that, in the preparation of potassium tert.butoxide, the incrustations of solid potassium hydroxide that form on the column packings can lead to the clogging of the column. This disadvantage can be remedied by the use of small amounts of caustic potash solution, but this considerably reduces the yield.
The procedure described in German Federal Pat. No. 968,903 does mention azeotropic distillation of the alcohol by means of a withdrawing agent. In the process described therein, however, the alcohol of the water-alcohol azeotrope that is distilled out must be constantly replaced, and a complex recovery process is necessary for that purpose.
The problem therefore existed of conducting the production of anhydrous potassium tert.butoxide from caustic potash solution and tert.butyl alcohol such that the reaction can be performed continuously in a distillation column without clogging or incrustation, and the unreacted input substances can be recovered in a simple manner. Furthermore, in the new process a very pure end product is to be obtained, whose KOH content is as low as possible, preferably less than 1% by weight.